Photocatalysts are capable of decomposition of organic substances and hydrophilization of a film surface and have been employed for uses including surface cleaning, deodorization, antimicrobial treatments, etc. Usually, catalyst particles, such as titanium oxide particles, are dispersed in a dispersion, and this dispersion is applied over a base and dried, whereby a film which has catalyst particles supported thereon is formed. In general, the catalytic effect increases according to the surface area of this film. Therefore, forming a catalyst-supporting film such that the surface of the film has an uneven structure has been considered (see Patent Documents 1 to 4).
Patent Document 1 discloses that a coating agent, which is a mixture of photocatalyst particles and a binder resin, is applied over a base which has a surface with minute unevenness so as to form a coating layer over the surface of the base. However, applying the coating agent over the uneven surface of the base in such a way leads to that the catalyst particles are caught in recessed portions so that the catalytic effects would not efficiently increase in some cases.
On the other hand, Patent Documents 2 to 4 disclose that a mixture (dispersion) is applied over a surface of a base, and thereafter, a surface of the mixture is deformed so as to have an uneven structure. Specifically, Patent Document 2 discloses forming an uneven structure which has a cleaning function and an antireflection function over a lens. Patent Document 3 discloses using a porous alumina layer formed by anodization as a mold so as to form a minute uneven pattern in an inorganic material which has a photocatalytic property. Patent Document 4 discloses a photocatalytic layer which has a moth-eye structure in order to realize a low reflection property. In this way, a surface of a film which has catalyst particles supported thereon is deformed into a porous shape, whereby the catalytic action can be increased.